When implementing interdomain multicast routing, which mechanism can be used to
advertise multicast sources in one domain to the other domains, allowing the RPs to build
interdomain multicast distribution trees?

A.
Multiprotocol BGP

B.
PIM

C.
MSDP

D.
Auto RP

E.
BSR

F.
MLD

Explanation:
Multicast Source Discovery Protocol
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM
sparse-mode domains.
MSDP allows multicast sources for a group to be known to all rendezvous point(s) (RPs) in
different domains.
Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains.
An RP in a PIM-SM domain has MSDP peering relationships with MSDP-enabled routers in
other domains.
Each peering relationship occurs over a TCP connection, which is maintained by the
underlying routing system.
MSDP speakers exchange messages called Source Active (SA) messages. When an RP learns
about a local active source, typically through a PIM register message, the MSDP process
encapsulates the register in an SA message and forwards the information to its peers. The
message contains the source and group information for the multicast flow, as well as any
encapsulated data. If a neighboring RP has local joiners for the multicast group, the RP
installs the S, G route, forwards the encapsulated data contained in the SA message, and
sends PIM joins back towards the source. This process describes how a multicast path can be
built between domains.